II. To describe the changes in phosphorylation of EGFR, her2, AKT kinase, MAPK, ER-Ser118,
and ER-Ser167 in tumor tissue after administration of tamoxifen and GW572016.

OUTLINE: This is a multicenter study.

Patients receive oral lapatinib and oral tamoxifen once daily on days 1-28. Courses repeat
every 28 days in the absence of disease progression or unacceptable toxicity.

Tumor tissue samples are collected at baseline and at 21 days after the beginning of study
therapy for phosphorylation of EGFR, her2, AKT kinase, MAPK, ER-Ser118, and ER-Ser167
analysis by IHC and Western blot assays.

After completion of study treatment, patients are followed at 1 month and then every 3
months thereafter.

Inclusion Criteria:

- At least 7 days since prior and no concurrent CYP3A4 inhibitors, including any of the
following:

- Clarithromycin

- Erythromycin

- Troleandomycin

- Itraconazole

- Ketoconazole

- Voriconazole

- Fluconazole (doses =< 150 mg/day allowed)

- Fluvoxamine

- Nefazodone

- Verapamil

- Diltiazem

- Cimetidine

- Aprepitant

- Proton pump inhibitors

- H2 blockers

- Grapefruit or grapefruit juice

- Bitter orange

- At least 14 days since prior and no concurrent CYP3A4 inducers, including any of the
following:

- Phenytoin

- Carbamazepine

- Phenobarbital

- Oxcarbazepine

- Efavirenz

- Nevirapine

- Rifampin

- Rifabutin

- Rifapentine

- Hypericum perforatum (St. John's wort)

- Modafinil

- At least 6 months since prior and no concurrent amiodarone.

- No concurrent gastric pH modifiers within 1 hour before and after lapatinib
administration.

- Histologically or cytologically confirmed primary adenocarcinoma of the breast:
Locally advanced or metastatic disease not amenable to curative surgery or
radiotherapy

- Tamoxifen-resistant disease, defined as 1 of the following: No response to initial
therapy (primary resistance); disease relapse or progression after showing an initial
response to therapy (secondary resistance)

- Disease progression, as documented by 1 of the following: CT scan, MRI, or x-ray;
increase in the number of bone lesions; increased pain in an area of known bony
metastasis AND >= 2 serial tumor marker elevations.

Name

Location

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